The incidence of type 2 diabetes (T2D) increases with age. Low‐grade inflammation in AT is implicated in development of insulin resistance and T2D. We conducted a study to determine if inflammatory responses are upregulated with age in AT. Results show that visceral AT from old mice had significantly higher expression of mRNA levels of IL‐1β, IL‐6, TNF‐α, and COX‐2 than those of young mice (263, 208, 165, and 73%, higher respectively). In determining the relative contribution of different components of AT to these age‐related changes, we found that adipocytes (AD) from old mice produced significantly more (2 to 3 folds) IL‐6 and PGE2 than those from young mice while no significant age difference was observed in their production by stromal vascular cells. There was no significant effect of age on number of Mϕ/g AT and Mϕ of either age group produced significantly more IL‐6 when incubated in conditioned medium from old AD compared to that of young. Blocking NF‐κB activation reduced IL‐6 production while addition of ceramide or sphingomyelinase increased IL‐6 production in young AD to a level comparable to that of old AD. Inhibiting de novo ceramide synthesis reduced IL‐6 production by AD. NF‐κB regulates expression of inflammatory products including COX‐2 and IL‐6. Ceramide was shown to increase COX‐2 expression in aged Mϕ through NF‐κB activation. Thus, these data suggest a potential role for ceramide and NF‐κB in the age‐related increase of AT inflammation. Further research is needed to fully determine the underlying mechanisms of the observed effects and their contribution to T2D in the aged. Supported by USDA #58‐1950‐9‐001 and NIA #R01 AG009140‐10A1.

Cui, Xue-Lin, Anna M. Schlesier, Elda L. Fisher, Carla Cerqueira, and Ronaldo P. Ferraris. Fructose-induced increases in neonatal rat intestinal fructose transport involve the PI3-kinase/Akt signaling pathway. Am J Physiol Gastrointest Liver Physiol 288: G1310 -G1320, 2005. First published February 3, 2005 doi:10.1152/ajpgi.00550.2004.-Expression of rat glucose transporter-5 (GLUT5) is tightly regulated during development. Expression and activity are low throughout the suckling and weaning stages, but perfusion of the small intestinal lumen with fructose solutions during weaning precociously enhances GLUT5 activity and expression. Little is known, however, about the signal transduction pathways involved in the substrate-induced precocious GLUT5 development. We found that wortmannin and LY-294002, inhibitors of phosphatidylinositol 3-kinase (PI3-kinase) specifically inhibited the increase in fructose uptake rate and brushborder GLUT5 protein abundance but not GLUT5 mRNA abundance. Perfusion of EGF, an activator of PI3-kinase, also resulted in a marked wortmannin-inhibitable increase in fructose uptake. Perfusion of fructose for 4 h increased cytosolic immunostaining of phosphatidylinositol-3,4,5-triphosphate (PIP 3), the primary product of PI3-kinase, mainly in the mid-to upper-villus regions in which the brush-border membrane also stained strongly with GLUT5. Perfusion of glucose for 4 h had little effect on fructose or glucose uptake and PIP 3 or GLUT5 staining. SH-5, an Akt inhibitor, prevented the increase in fructose uptake and GLUT5 protein induced by fructose solutions, and had no effect on glucose uptake. The PI3-kinase/Akt signaling pathway may be involved in the synthesis and/or recruitment to the brush border of GLUT5 transporters by luminal fructose in the small intestine of weaning rats. Increases in fructose transport during the critical weaning period when rats are shifting to a new diet may be modulated by several signaling pathways whose cross talk during development still needs to be elucidated. development; glucose; intestine; epidermal growth factor; mucosa BECAUSE OF DRAMATIC INCREASES in consumption of soft drinks and fruit juices, per capita consumption of fructose in the United States has increased by 10 times in 30 yr to almost 60 g fructose per day (4, 39). Paralleling this remarkable increase in fructose consumption is an alarming increase in incidence of obesity and in prevalence of type II diabetes (4,14). What makes this correlation disturbing is that per capita fructose consumption in very young children has increased faster than that of the general population and in the 1980s was already ϳ30 -40 g fructose per day representing 10% of their energy intake (39). The top 10th percentile of subjects in all age groups typically consume approximately two times more fructose, exposing this particular age group (1-6 yr of age) to potential metabolic derangements caused by excessive fructose consumption. There are very few studies on physiological adaptations to excessive fructose consumpti...

The intestinal brush border fructose transporter GLUT5 (SLC2A5) typically appears in rats after weaning is completed. However, precocious consumption of dietary fructose or in vivo perfusion for 4 h of the small intestine with high fructose (HF) specifically stimulates de novo synthesis of GLUT5 mRNA and protein before weaning is completed. Intermediary signals linking the substrate, fructose, to GLUT5 transcription are not known but should also respond to fructose perfusion. Hence, we used microarray hybridization and RT-PCR to identify genes whose expression levels change during HF relative to high-glucose (HG) perfusion. Expression of GLUT5 and NaPi2b, the intestinal Na+-dependent phosphate transporter, dramatically increased and decreased, respectively, with HF perfusion for 4 h. Expression of >20 genes, including two key gluconeogenic enzymes, glucose-6-phosphatase (G6P) and fructose-1,6-bisphosphatase, also increased markedly, along with fructose-2,6-bisphosphatase, an enzyme unique to fructose metabolism and regulating fructose-1,6-bisphosphatase activity. GLUT5 and G6P mRNA abundance, which increased dramatically with HF relative to HG, alpha-methylglucose, and normal Ringer perfusion, may be tightly and specifically linked to changes in intestinal luminal fructose but not glucose concentrations. G6P but not GLUT5 mRNA abundance increased after just 20 min of HF perfusion. This cluster of gluconeogenic enzymes and their common metabolic intermediate fructose-6-phosphate may regulate fructose metabolism and GLUT5 expression in the small intestine.

Fructose in the lumen of the small intestine is transported across the brush border membrane by GLUT5, then across the basolateral membrane by GLUT2, which also transports glucose. Diets containing high fructose (HF) specifically enhance intestinal GLUT5 expression in neonatal rats, but there is little information concerning the dietary regulation of GLUT2 expression during early development. In this study, we perfused for 1-4 h 100 mM fructose, glucose (HG), alpha-methylglucose, or mannitol solutions into the jejunum of anaesthetized 20-day-old rat pups. GLUT2 mRNA abundance increased only in HF- and HG-perfused intestines, an effect inhibited by actinomycin D but not by cycloheximide. Bypassed (Thiry-Vella) intestinal loops were constructed, then pups were fed either HF or low-carbohydrate diets for 5 days. GLUT2 mRNA abundance increased significantly in both bypassed and anastomosed intestines of Thiry-Vella pups fed HF. In contrast, GLUT5 mRNA abundance increased only in the anastomosed segment. In sham-operated pups, GLUT2 and GLUT5 mRNA abundance increased in both intestinal regions that corresponded to the bypassed and anastomosed regions of Thiry-Vella pups. SGLT1 mRNA abundance was independent of diet and intestinal region in both Thiry-Vella and sham-operated pups. Unlike GLUT5 expression, which is regulated at the level of transcription only by luminal fructose, GLUT2 mRNA expression is transcriptionally regulated by luminal fructose and glucose as well as by systemic factors released during their absorption.

Intestinal fructose transporter (GLUT5) expression normally increases significantly after completion of weaning in neonatal rats. Increases in GLUT5 mRNA, protein, and activity can be induced in early weaning pups by precocious consumption of dietary fructose or by perfusion of the small intestine with fructose solutions. Little is known about the signal transduction pathway of the dietary fructose-mediated increase in GLUT5 expression during early intestinal development. Recent microarray results indicate that key gluconeogenic enzymes modulated by cAMP are markedly upregulated by fructose perfusion; hence, we tested the hypothesis that cAMP plays an important role in regulating intestinal fructose absorption by simultaneously perfusing adenylyl cyclase, phosphodiesterase, or protein kinase A (PKA) inhibitors along with fructose. Intestinal fructose uptake rates increased by 100% in rat pups perfused with 8-bromo-cAMP. Simultaneous fructose and dideoxyadenosine (DDA; inhibitor of adenylyl cyclase) perfusion completely inhibited increases in fructose uptake rate induced by perfusion with fructose alone. Fructose perfusion increased intestinal mucosal cAMP concentrations by 27%, but simultaneous perfusion of fructose and DDA inhibited the fructose-induced increase in cAMP. However, GLUT5 and sodium-glucose cotransporter (SGLT1) mRNA abundance and glucose transport rates were each not significantly affected by 8-bromo-cAMP and DDA. Moreover, simultaneous perfusion of the small intestine with fructose and PKA inhibitor or N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamid. 2HCl, both inhibitors of PKA, did not prevent the fructose-induced increases in GLUT5 mRNA abundance and fructose uptake rate. Cyclic AMP appears to modulate fructose transport without affecting GLUT5 mRNA abundance, and without involving PKA.